Ch22: Human Evolution

Evolution Vs. Intelligent Design Change in heritable traits within a population over successive generations Supported by scientific evidence Intelligent Design Concept that “certain features of the universe and of living things are best explained by an intelligent cause” Can not be supported or rejected by research

Geological Time

Chemical Evolution Atmospheric gases reacted and produces small organic molecules Stanley Miller performed an experiment to support this hypothesis Small organic molecules joined to produce organic macromolecules Organic macromolecules formed the first Protocell. Lipid-protein membrane Heterotroph – takes in preformed food Fermenter- created energy without oxygen Protocells incorporated RNA (& then DNA) to create a True cell. Cell was able to reproduce & pass on its genetic information.

Biological Evolution Biological evolution is a change in life forms between generations. Two aspects of biological evolution: Common descent – all living descended from a common ancestor Explains unity of all living things (i.e. all living things are made up of cells and have the same biochemistry) Adaptation – modification in structure, function, or behavior to better suit the environment Explains the diversity of life

Charles Darwin A naturalist that formulated the theory of evolution based on the following evidence: Biogeographical – even though there were suitable environments for certain plants & animals they were not distributed everywhere. Anatomical Homologous structures – anatomical parts that are similar, but have different functions; these anatomical similarities indicate common descent. Analogous structures – have the same function, but are anatomically different; thus, there is no common descent Fossils – remains or traces of past life that has been preserved in the earth’s crust.

Homologous Structures

Additional Evidence Biochemical Evidence – almost all living organisms use the same basic biochemical molecules. DNA – genetic information Organisms that are closely related have a higher percentage of similar DNA Proteins – same 20 amino acids ATP – molecule for energy

Evolutionary Mechanisms Natural Selection - the process by which a species becomes adapted to its environment. Sexual Selection – the process by which certain individuals are chosen to mate. Genetic Drift – random changes in gene frequency in a population

Evolutionary Mechanisms Evolutionary Mechanisms are dependent on: Mutations – changes in chromosome structure Genetic Recombination – changes in alleles combinations often due to crossing-over Gene flow – movement of alleles of genes into or out of a population by migration and interbreeding.

Natural Selection Variation - physical variations can be passed from generation to generation Competition - the environment “selects” these better adapted members to have offspring and to pass on this characteristic Adaptation - subsequent generation include more individuals that are adapted in the same way to the environment.

Sexual Selection Intrasexual competition – same sex individual fight to mate with females Intersexual competition – females (or males) choose certain mates based on certain characteristics.

Human Evolution: Humans are Primates Characteristics of Primates: Grasping fingers and toes, some with opposable thumbs Well-developed brain Nails Single birth Extended period of parental care Emphasis on learned behavior Two Suborders: Prosimians—lemurs, tarsiers, and lorises. Anthropoids—monkeys, apes, and humans

Evolution of Hominids Hominid – humans Family branch Bipedal posture (walking on two feet) Flat face Brain size Australopithecines - a group of individuals that evolved and diversified in Africa. Hominids lived about 3 MYA Walked erect Small brain compared to us, but large brain compared to other primates Limb proportions are ape-like Australopithecus africanus with its large brain is the best ancestral candidate for early Homo

Evolution of Homo Homo habilis - may be the ancestor to modern humans (2.0-1.9 MYA) Made tools Large brain Dentition Omnivores (plant gatherers and hunters) May have had the rudiments of a culture Homo erectus – may have evolved from Homo habilis (1.9 -.3 MYA) Striding gait Made well-fashioned tools Control of fire Migrated into Europe and Asia

Evolution of Modern Humans Multiregional Continuity Hypothesis – evolution of modern humans was essentially similar in many different places. Out-of-Africa Hypothesis – evolution of H.sapiens evolved from H.erectus only in Africa and then H.sapiens migrated to Europe & Asia

We are one Species Biological definition of a species – Any group of organisms able to interbreed and bear fertile offspring.